Download Coral Bleaching

Coral Bleaching
www.ogp.noaa.gov
Why Bleaching?
Sun exposed areas bleach first
Photosynthesis
(normal conditions)
Photosynthesis under thermal stress
(Photoinhibition bleaching model)
Thermal thresholds
(Temperatures at which bleaching occurs)
Hoegh-Guldberg 1999
La Niña
El Niño
Tahiti Sea Surface temperature
Hoegh-Guldberg 1999
Number of reefs severely bleaching
Hoegh-Guldberg 1999
1998 Massive Bleaching
Question 1:
• Why are corals growing so close to
their thermal limit?
Predicted evolution SST
(Global coupled atmosphere-ocean-ice model)
Hoegh-Guldberg 1999
Question 2:
• Why are corals growing so close to
their thermal limit?
• Why are there few reports of coral
bleaching before 1979?
Predicted evolution SST
(Global coupled atmosphere-ocean-ice model)
Hoegh-Guldberg 1999
Question 3:
• Why are corals growing so close to
their thermal limit?
• Why are there few reports of coral
bleaching before 1979?
• Will coral bleaching increase in the
future?
Hoegh-Guldberg 1999
Possible scenarios of increasing SST
• Strategy shift:
– Hardy spp. replace sensitive spp.
• Tolerance: Corals acclimate + evolve
– spp. with highest genetic variability expected to
survive
• Phase shift: corals are replaced by algae
– Already occurring in many regions!
Simple Model
Model with interspecific
differences in thermal
thresholds
Model with thermal threshold
differences + acclimation & evolution
Hughes et al. 2003
Interspecific bleaching Susceptibility
Diverse Communities
Monospecific communities
Interspecific Bleaching Susceptibility
Raiatea, French Polynesia (May 2002)
Hughes et al. 2003
Coral species boundaries
(geographical differences)
1- Local Temperature differences
2- Genetic Variability differences
Low-Isolated endemic populations
High-Central and Mainland populations
Hughes et al. 2003
Facts on the future of Coral Reefs due
to Global warming
• Few indications that coral acclimation /
rapid evolution is occurring
• Oceans warming 2oC / 100 years
• Annual massive bleaching events by
2030-2070
• Phase shift away from coral dominated
communities by 2050
• Economical impact of Trillions of $,
affecting 100’s of million humans
Coral-Algae Phase Shift (Jamaica)
1984
199592%
Algae
3%
Coral (% cover)
53%
4%
Herbivory in Coral Reefs
Coral reef herbivores?
• Green Turtles
– Ecologically extinct
• Manatees & Dugongs
– Ecologically extinct
• Parrotfish (& surgeonfish)
– Generally overfished
• Sea Urchins
– Variable abundance (diseases & predation)
Jamaican History 101
•
•
•
•
•
1492: 16 million Green Turtles (Caribbean)
1688-1730: 13000 turtles/year (slave food)
1730: 6.5 million Turtles (Caribbean)
1800: Turtle fishery crashes, Fish fishery develops
1881: Jamaica imports 85% of its fish
(local overfishing)
• 1962: Historical high fishery catches (15% local origin)
(local overfishing still)
No Turtles, No manatees, Very few parrotfish
ONLY SEA URCHINS LEFT
(Diadema antillarum)
Jamaican History 102
• 1980: Hurricane Allen
• 1983: Diadema die-off across Caribbean (99% mortal.)
NO HERBIVORES LEFT!
• Late 1980’s: Shift to Algal Domination
• 1991: Hurricane Gilbert
• Today:
– Algae dominate reefs
– Extensive overfishing of herbivore fish species
– Slow and patchy recovery of Sea Urchins populations
% reef sites
Historical coral reef
community changes
P = Prehuman
H = Hunter Gatherer
A = Agricultural
CO+CD = Colonial
M1 = Modern
M2 = Present
Historical coral reef degradation
Increase Coral Diseases
Massive Bleaching
OVERFISHING
Principle 15 of the Rio
Declaration
• “Where there are threats of serious or
irreversible damage, lack of full scientific
certainty shall not be used as a reason for
postponing cost-effective measures to
prevent environmental degradation.”